In crop protection, it is desirable in principle to increase the specificity and the reliability of the action of active compounds. In particular, it is desirable for the crop protection product to control the harmful plants effectively and, at the same time, to be tolerated by the useful plants in question.
Pyroxasulfone has been described in EP-A 1364946 and US 2005/0256004.
Although pyroxasulfone is a highly effective pre-emergence herbicide, its activity at low application rates is not always satisfactory. Moreover, pyroxasulfone is known to have only poor post-emergence activity (Y. Yamaji et al., “Application timing and field performance of KIH-485”, Conference Abstract I-1-ii-12B of 11. IUPAC International Congress of Pesticide Chemistry, 2006 Kobe, Japan). Apart from that, its compatibility with certain dicotyledonous crop plants such as cotton, sunflower, soybean, brassica crops such as canola and oilseed rape and some graminaceous plants such as rice, wheat, rye and barley is not always satisfactory, i.e. in addition to the harmful plants, the crop plants are also damaged to an extent which is not acceptable. Though it is in principle possible to spare crop plants by lowering the application rates, the extent of the control of harmful plants is naturally also reduced.
It is known that combined application of certain different herbicides with specific action might result in an enhanced activity of a herbicide component in comparison with a simple additive action. Such an enhanced activity is also termed a synergism or synergistic activity. As a consequence, it is possible to reduce the application rates of herbicidally active compounds required for controlling the harmful plants.
WO 2005/104848 describes compositions containing a herbicidal 3-sulfonylisoxazoline compound such as pyroxasulfone and a herbicide-antagonistically active amount of a safener. Similar compositions are known from WO 2007/006509.
US 2005/256004, for example, discloses that in a pre-emergence treatment, joint application of certain herbicidal 3-sulfonylisoxazoline compounds such as pyroxasulfone with atrazine or cyanazine results in an increased overall herbicide action against certain monocotyledonous and dicotyledonous annual broadleaf weeds (lambsquarter, green foxtail, velvetleaf) in comparison with a simple expected additive action.
WO 2006/097322 discloses a herbicidal composition comprising pyroxasulfone and a second herbicide selected from tembotrione, topramezone and 4-hydroxy-3-[[2-[(2-methoxyethoxy)methyl]-6-(trifluoromethyl-3-pyridinyl]carbonyl]bicyclo[3.2.1]oct-3-ene-2-one.
WO 2006/097509 discloses a herbicidal composition comprising a herbicidal 3-sulfonylisoxazoline compound such as pyroxasulfone and a phenyluracil compound.
Unfortunately, it is usually not possible to predict synergistic activity for combinations of known herbicides, even if the compounds show a close structural similarity to known synergistic combinations.